I have a user who edits technical materials. She uses MS Word's Custom Dictionary all the time for spelling; it has grown very large, and is now making spell check very slow.

All of the advice I've read online says to disable the custom dictionary. This is an easy solution, but is not workable for the user, because she actually needs this dictionary.

So, is there any way to optimize the custom dictionary and/or Word itself, so that a large dictionary file doesn't slow things down quite so badly?

Many thanks.

Update after suggestions:

I ran contig on the file, and it reports just 1 frag, so that's not the issue I think.

The file is 9.95KB -- 1,117 lines, each consisting of just a single word. I viewed the file using Notepad and none of the lines seems corrupted, strange, or overly long (no line seems to be over 10 chars or so).

Both of your suggestions were helpful so I will upvote both; any further tips would be most welcome.


You may check the fragmentation of this file as it may be causing some slowdowns.

To do that grab Contig on Sysinternals site and use it like this to get the number of fragments of that file:

contig.exe -a "%USERPROFILE%\Application Data\Microsoft\UProof\CUSTOM.DIC"

Note the "Average fragmentation" value and if it is above 1 frag/file run that command again, this time without the "-a" argument:

contig.exe "%USERPROFILE%\Application Data\Microsoft\UProof\CUSTOM.DIC"

Note that if the average number of fragments by file is low the slowdowns are probably not caused by it.

Word seems to have a problem with "big" custom dictionnaries and that reflects a bad development practice, every modern app should handle multi-megabytes files like this gracefully.

  • 1
    Awesome utility! Didn't know about contig at all. Tried it, reports just 1 frag. Updated OP with info. Any other ideas would be great :) – ezuk Nov 22 '11 at 17:42

Even a huge Word Custom Dictionary is only about 64KB in size, and it's a plain text file.

It's usually located in %APPDATA%\Microsoft\UProof, and it's called CUSTOM.DIC.

Perhaps it's corrupted? Have you done any disk checks (chkdsk) to ensure the file system is OK?

You should be able to visually scan it in a text editor and see any crazy/corrupted lines. :)

Since it's plain text, you can rename it (with Word closed), make a new text file name CUSTOM.DIC, add a few words via Notepad or another text editor, and try Word again.

If that works OK, then perhaps try copying/pasting the contents of the old file over top of the new file (again using Notepad), and see how that works.

  • Thanks, but no corrupted lines appear in the file. I can't 'chkdsk' at the moment because the user absolutely must work (urgent work), but I may try that later on. I updated the original post with further info. – ezuk Nov 22 '11 at 17:41

Okay, we kept on trying to resolve it and eventually found out what caused it: The Word file that was being spell-checked was apparently somehow corrupted.

The content displayed, but there were some incorrect fonts and other weird artefacts. When the user switched to a different file, the issue was resolved.

Thanks for the helpful suggestions, and I hope someone finds this thread handy in the future. :)

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